Blender export fbx file holes in mesh deformed
The problem are the faces with more than 4 edges (ngons), in your case, most of them have 6 edges.



What you can do is select all the faces around the windows, the press CTRL+T to convert them to triangles and then ALT+J to convert them to quads.



Notice how I set Max Face Angle and Max Sharp Angle to 180º.

You also should remove unnecessary vertices like these:

By pressing ALT+M to merge them before converting the ngons to tris then to quads.